1. Field of the Invention
The present invention relates to an inkjet recording method and a recording product, more specifically, to an inkjet recording method including attaching two liquids, i.e., a reaction liquid and an ink composition, to a recording medium having an absorbing layer of a paper support with low water absorption to perform printing, and a recording product.
2. Invention of Related Art
An inkjet recording method is a printing method in which droplets of an ink composition are allowed to fly and deposited on a recording medium such as paper to perform printing. The inkjet recording method facilitates a reduction in size, an increase in operating speed, a reduction in noise, a reduction in power consumption, and color printing. Furthermore, the inkjet recording method has a feature in which non-contact printing can be performed for a recording medium, and is thus used for various applications. For example, various images are formed by recording apparatuses using the inkjet recording method.
In particular, for industrial applications, images formed by full-color inkjet recording method can have good quality comparable to those of multicolor printing using printing plates and silver salt photography. In the case where small batches of many different prints are produced, use of the inkjet recording method has recently been growing because the inkjet recording method is inexpensive compared with usual multicolor printing.
In general, the ink composition used in the ink jet recording method is an aqueous ink composition which contains water as a main component, a colorant, and a humectant for preventing clogging, and other components and which has a low viscosity and a high water content. Thus, usually, high-water-absorption specialized inkjet paper is used as a recording medium.
High-water-absorption specialized inkjet paper includes an absorption layer composed of fine powdered silica or alumina on a surface of the paper. The absorption layer can absorb ink instantaneously even when recording is performed with an ink composition having a high water content, so that it is possible to achieve satisfactory print quality free from, for example, feathering or color bleeding. However, for industrial printing users who want to achieve a further reduction in print cost, the use of expensive fine powdered silica or alumina limits applications.
On the other hand, an example of an inexpensive medium is coated paper (also referred to as “coated printing paper”, “coated paper for printing”, and “proofing base”) as a low-water-absorption recording medium. Coated paper is a combined sheet in which coating color, a type of paint, is applied on either or both sides of base paper in order to improve printability. Coated paper is specifically used as printing paper. Coated paper is used for a recording method using a high-viscosity ink composition (ink with a low water content) and an ink composition containing a solvent. Demands for several millions of tons of coated paper every year result in mass-production equipment, thus leading to the supply of high-quality coated paper at very low cost.
Although the high-viscosity low-water-content ink composition provides a good-quality image on a low-water-absorbable or non-absorbable recording medium, it is technically difficult to ensure reliability such as recoverability from clogging and ejection stability. Furthermore, as the inkjet recording method, printing apparatuses and printing methods are limited. In addition, the ink composition containing a solvent is composed of a low-water-solubility or insoluble raw material (e.g., a lipophilic organic solvent such as toluene) and thus provides excellent image quality, abrasion resistance, and durability and has an excellent quick drying property. However, some organic solvents contained therein may be toxic for animals and plants and may adversely affect the health of personnel due to air pollution by high-volatile organic solvent (VOC); hence, it is inconvenient to handle such solvents from the viewpoints of achieving safety and environmental friendliness.
Meanwhile, an aqueous low-viscosity ink composition commonly used in inkjet recording is easy to ensure safety, environmental friendliness, and ejection reliability for an inkjet recording method. However, when recording is performed on a recording medium such as coated paper that does not include a thick absorbing layer unlike the specialized inkjet paper, a deterioration in image quality, e.g., feathering, color bleeding, and uneven printing, reductions in abrasion resistance and quick drying property are caused because of its poor water absorption. It is thus considered that coated paper is not suitable as a recording medium.
On the other hand, a new ink jet recording method has been recently proposed. The new method includes applying a polyvalent metal salt solution onto a recording medium and then applying an ink composition containing a dye having at least one carboxyl group (Patent Document 1). According to this method, polyvalent metal ions combine with the dye to form an insoluble composite which can provide an image having water resistance and a high quality free from color bleeding.
Furthermore, an ink jet recording method has been proposed in which a color ink containing at least a surfactant or a penetrable solvent and a salt for imparting a penetrating property is used in combination with a black ink which cooperates with the salt to cause thickening or agglomeration, thereby providing a high-quality color image having a high image density and free from color bleeding (Patent Document 2). More specifically, in this method, two liquids, i.e., a first liquid containing a salt and a second liquid of an ink composition, are printed to provide a good image.
In addition, other ink jet recording methods in which two liquids are printed have been proposed (Patent Document 3 to 7).
Here, the following items are required for the inkjet recording method in which two liquids are printed on a low-water-absorption recording medium (e.g., coated paper):
1) A reaction liquid can be evenly applied to a low-water-absorption recording medium such as coated paper.
2) Reaction of the reaction liquid and an ink composition prevents the occurrence of feathering, color bleeding, and uneven printing.
3) A recording product has excellent abrasion resistance (the two liquids have excellent adhesion and bondability to the recording medium).
4) After the application of the liquids to the recording medium, the liquids can be readily dried.
5) The characteristics of the reaction liquid and the ink composition are not degraded with time (excellent storage stability)
6) The reaction liquid and the ink composition can be ejected in an inkjet manner, and a head is not clogged in practical use.
In the related art, an inkjet recording method that satisfies all the above requirements is not provided. In particular, disadvantageously, in the case where the reaction liquid does not have uniform wettability for the recording medium, the concentration distribution of a colorant in the ink composition printed after printing the reaction liquid is liable to occur, i.e., uneven printing is liable to be performed. Furthermore, in the case where the reaction liquid does not have uniform wettability, agglomerates of the reaction liquid and the ink composition are unevenly distributed, so that the resulting resin film is uneven. This increases the resistance when the film is rubbed, thereby disadvantageously reducing abrasion resistance.